To address and overcome inherent existing limitations in prior art radio frequency identification (RFID) tags with respect to cost, data capacity and reliable range, a new RFID tag technology has been developed. This new technology utilizes surface acoustic wave (SAW) devices as identification tags and is described in detail in U.S. patent application Ser. No. 10/066,173, entitled “Surface Acoustic Wave Identification Tag Having Enhanced Data Content and Methods of Operation and Manufacture Thereof,” Harhnann, Clinton S. (“Hartmann One”), commonly assigned with the invention and incorporated herein by reference. The principles used to encode data on SAW tags involving simultaneous phase and time shift modulation is described in detail in U.S. patent application Ser. No. 10/062,833, entitled “Modulation by Phase and Time Shift Keying and Method of Using the Same,” Hartmann, Clinton S. (Hartmann-Two), also commonly assigned with the invention and incorporated herein by this reference. The principles used to encode data by combining multi-pulse per group modulation with simultaneous phase and time shift modulation is described in detail in U.S. patent application Ser. No. 10/062,894, entitled “Modulation by Combined Multi-pulse per Group with Simultaneous Phase and Time Shift Keying and Method of Using the Same,” Hartmann, Clinton S. (Hartrnann-Three), also commonly assigned with the invention and incorporated herein by reference. Additional pertinent information regarding SAW identification tags and SAW identification tag readers is set forth in detail in U.S. patent application Ser. No. 10/066,249, entitled “Reader for a High Information Capacity Saw Identification Tag and Method of Use Thereof,” Hartmann, Clinton S. (“Hartmann Four”), again commonly assigned with the invention and incorporated herein by reference.
An interrogated RFID tag reflects or retransmits a radio signal in response to an interrogation signal. The returned or reply signal contains the data that, when decoded, identifies the tag and any object with which the tag is associated. A SAW device used as an identification tag can be encoded with a large amount of data. When encoded with 64 or 96 bits of data, in accordance with certain electronic product code (EPC) specifications, if such tags are to be useful, a reliable system and procedure to accurately identify the tag from a distance is required.
The problem can be best understood in the context of a user that has a large number of objects, each with its own unique identification tag. In order to identify a specific object among the large number of objects, the user will send an interrogation signal to be simultaneously received by a tag on each of the objects. When each responds to the interrogation signal, there will be a large quantity of data from which the signal from a single tag must be isolated and identified. Thus, it is important for that SAW tags be encoded in a manner that tags can be readily distinguished from one another. A system is needed that can be used to encode SAW tags with unique data that can readily be distinguished from the data encoded on other SAW tags.
Accordingly, what is needed in the art is a reliable system for determining the unique identifier encoded on a SAW identification tag that can be readily decoded to identify the object with which it is associated.